1. Field of the Invention
The invention relates a coupling structure for cryogenic hydrocarbon transfer pipes, comprising:                a first and a second cryogenic transfer pipe section each having a metal wall and a flexible pipe section interconnecting the first and second sections,        a hinging support frame comprising        a first set of arms connected with a base end to the first pipe section,        a support ring around the flexible pipe section hingingly attached to hinge end parts of the first set of arms, the first set of arms being pivotable around a first axis, and        a second set of arms connected with a base end to the second pipe section and with a hinge end part hingingly attached to the support ring, the second set of arms being pivotable around a second axis, which is transverse to the first axis.        
2. Description of Related Art
From U.S. Pat. No. 4,097,072 it is known to interconnect rigid conduit sections of an oil transfer pipe by a flexible hose. The flexible hose extends within a cage-shaped cardan joint, the cardan joint transferring the large static and dynamic mechanical loads from one rigid conduit section to the other whilst allowing the conduit sections to pivot with respect to one another around two perpendicular axes. The flexible conduit provides freedom of movement and forms a fluid-tight connection without transferring significant forces.
When transferring cryogenic fluids, such as Liquefied Petroleum Gas (LPG) or Liquefied Natural Gas (LNG), the temperature of the conduit sections can become very low, such as minus 130° C. Special provisions need to be taken for the flexible hose in order to prevent it from becoming brittle and cracking after a few bending cycles. Also the structural members of the cardan, or gimbal couplings will suffer from low temperatures. Especially during start-up and shut down of cryogenic fluid transfer, the temperature differences will cause relatively large local contractions and expansions which may cause the cardan joint to fail due to misalignment of the hinges which can no longer pivot around their axes and hence become jammed. Another adverse effect on the cardan joint caused by the low temperatures is that the hinges could freeze together due to ice formation in the wet offshore environment.